Typical vehicular and roadside units within a wireless dedicated short range communication (DSRC) system exchange both high priority/low latency data (e.g., emergency warnings), and low priority/best effort data (e.g., map updates). An example of such a system is specified in the IEEE 1609 family of standards for wireless access in vehicular environments (WAVE). Such systems employ a series of radio channels in the 5 GHz band, one of which is designated a control channel and others designated service channels. Data packets (transmission units) may be of varying sizes. A contention-based scheme is used for channel access.
All devices are required to periodically tune to the control channel to exchange information of general interest. At other times, devices may operate on any of the service channels to exchange information of interest to a subset of the devices. These times are known as the control channel interval and service channel interval respectively. Between each control channel interval and service channel interval is a guard interval, reserved for radio frequency tuning, where transmissions are not allowed. The effect of this is that access to any given channel is discontinuous and is available only within a channel interval with a known end time. This is illustrated in FIG. 1.
As shown, when data arrives at a device for transmission on one of the channels, the data is queued. Any of several factors will affect the time the data may actually be transmitted.                The wireless system may impose medium access control protocols, such as those specified in IEEE Std. 802.11p, Information technology—Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements—Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: Wireless Access in Vehicular Environments (WAVE)—DRAFT STANDARD, the entire content of which is hereby expressly incorporated by reference.        The wireless system may specify prioritization of data, such that higher priority data has precedence and is more likely to be transmitted first.        A device with a single-channel radio can only operate on one channel at a given instant. If it has control channel data arriving for transmission during the service channel interval (e.g., T1 in FIG. 1), the data must be queued until at least the beginning of the next control channel interval. Likewise for service channel data arriving during the control channel interval.        Since data can not be transmitted during the guard interval, no transmission should start at a time that would cause the transmission to overlap the guard interval.        
Some systems employ a quality of service-based queue maintenance structure specified in IEEE Std. 802.11e, Information technology—Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements—Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: Amendment: Medium Access Control (MAC) Quality of Service Enhancements, the entire content of which is hereby expressly incorporated by reference. However, this mechanism does not account for performance improvements that can be made to accommodate the transmission disruptions imposed by the non-continuous channel availability of the system.